1. Field of the Invention
The present invention relates to a method and a device for producing steel castings in slab form. Specifically, the present invention relates to a method for controlling the taper of narrow faces of a liquid-cooled plate-type mold for the production of steel castings, wherein the narrow faces can be adjusted between wide faces.
2. Description of the Related Art
In the continuous casting of steel in liquid-cooled molds formed of individual plates for the production of castings in slab form, there is originally formed in the mold, due to the low thermal conductivity of the steel, only a thin casting shell of solidified melt. It is known and desired by the continuous caster that the casting shell is produced in the mold as far as possible in a thickness which is uniform over its circumference, since this thin casting shell must withstand, outside the mold, the ferrostatic pressure of the melt which is present within it. The person skilled in the art furthermore knows that the development of the thickness and of the uniformity of the solidified casting shell at the exit from the mold is dependent on a number of factors such as the casting rate, temperature of the steel, geometry, material and taper of the mold and, last but not least, the type and composition of the lubricant which is applied to the liquid-steel level or the meniscus and is to reduce the friction between casting shell and mold.
The fact that time and again casting breakouts occur, i.e. the melt emerges through the casting shell, which leads to an interruption in the casting, shows that this problem has not yet been reliably overcome, although there are any number of suggestions as to how to solve this problem.
Thus, proposals are known from DE 31 10 012 C1, EP 0 114 293 B1, DE 33 09 885 A1, DE 39 08 328 A1 which attempt, by adjustment of the taper of the narrow faces of the mold, to determine or influence the cooling conditions in the mold and thus the formation of the casting shell.
On the other hand, it is known from DE-OS 15 08 966, DAS 23 19 323, DE-PS 23 20 277, DE-PS 24 40 273, and DE 34 23 475 C2 to control the thickness of the casting shell by measurements of the temperature of the mold wall or of the quantity of heat discharged from the mold.
All known methods have in common that the mold, or the entire plant, is controlled on the basis of measured values compared with predetermined desired values, it remaining open, however, to what extent the predetermined desired values take into account the actual circumstances or requirements.